Read the excerpt from ivanhoe.

but, confident in their armor of proof, and in the cover which their situation afforded, the followers of front-de-boeuf, and his allies, showed an obstinacy in defense proportioned to the fury of the attack and replied with the discharge of their large cross-bows, as well as with their long-bows, slings, and other missile weapons, to the close and continued shower of arrows; and, as the assailants were necessarily but indifferently protected, did considerably more damage than they received at their hand.

which word is an appropriate synonym for the word obstinacy as it is used in the excerpt?